<html><head>
    <meta charset="utf-8">
    <title>Canvas鼠标移动粒子效果动画</title>

    <style>
        body,
        html{
            margin: 0;
            padding: 0;
            border: 0;
            font-family: 'Nunito', sans-serif;
        }

        body{background:#000;}

        canvas{
            margin: 0;
            padding: 0;
            display: block; /*  ˉ\_(ツ)_/ˉ  */
            touch-action: none;
        }
        h1{
            position: absolute;
            top: 50%;
            left: 0;
            margin: auto;
            width: 100%;
            text-align: center;
            color:#fff;
        }
    </style>

</head>
<body>

<h1>
    别害羞, 把鼠标挪过来!
</h1>

<canvas height="843" width="1303"></canvas>

<script>
    var canvas = document.querySelector('canvas');
    canvas.height = window.innerHeight;
    canvas.width = window.innerWidth;
    c = canvas.getContext('2d');

    window.addEventListener('resize', function(){
        canvas.height = window.innerHeight;
        canvas.width = window.innerWidth;

        initCanvas();
    })

    var mouse = {
        x: undefined,
        y: undefined
    }
    window.addEventListener('mousemove',
        function (event) {
            mouse.x = event.x;
            mouse.y = event.y;
            drawCircles();
        }
    )
    window.addEventListener("touchmove",
        function (event) {
            let touch = event.touches[0];
            mouse.x = touch.clientX;
            mouse.y = touch.clientY;
            drawCircles();
        }
    )

    function Circle(x, y, radius, vx, vy, rgb, opacity, birth, life){
        this.x = x;
        this.y = y;
        this.radius = radius;
        this.minRadius = radius;
        this.vx = vx;
        this.vy = vy;
        this.birth = birth;
        this.life = life;
        this.opacity = opacity;

        this.draw = function() {
            c.beginPath();
            c.arc(this.x, this.y, this.radius, Math.PI * 2, false);
            c.fillStyle = 'rgba(' + rgb +','+ this.opacity +')';
            c.fill();
        }

        this.update = function(){
            if (this.x + this.radius > innerWidth || this.x - this.radius < 0) {
                this.vx = -this.vx;
            }

            if (this.y + this.radius > innerHeight || this.y - this.radius < 0) {
                this.vy = -this.vy;
            }

            this.x += this.vx;
            this.y += this.vy;

            this.opacity = 1- (((frame - this.birth) * 1) / this.life);

            if (frame > this.birth + this.life){
                for (let i = 0; i < circleArray.length; i++){
                    if (this.birth == circleArray[i].birth && this.life == circleArray[i].life){
                        circleArray.splice(i, 1);
                        break;
                    }
                }
            } else{
                this.draw();
            }
        }

    }

    var circleArray = [];

    function initCanvas() {
        circleArray = [];
    }

    var colorArray = [
        '355,85,80',
        '9,80,100',
        '343,81,45'
    ]

    function drawCircles(){
        for (let i = 0; i < 6; i++) {
            let radius = Math.floor(Math.random() * 4) + 2;
            let vx = (Math.random() * 2) - 1;
            let vy = (Math.random() * 2) - 1;
            let spawnFrame = frame;
            let rgb = colorArray[Math.floor(Math.random() * colorArray.length)];
            let life = 100;
            circleArray.push(new Circle(mouse.x, mouse.y, radius, vx, vy, rgb, 1, spawnFrame, life));

        }
    }

    var frame = 0;
    function animate() {
        requestAnimationFrame(animate);
        frame += 1;
        c.clearRect(0, 0, innerWidth, innerHeight);
        for (let i = 0; i < circleArray.length; i++ ){
            circleArray[i].update();
        }

    }

    initCanvas();
    animate();

    // This is just for demo purposes :
    for (let i = 1; i < 110; i++) {
        (function (index) {
            setTimeout(function () {
                mouse.x = 100 + i * 10;
                mouse.y = 100;
                drawCircles();
            }, i * 10);
        })(i);
    }
</script>


</body></html>